The invention is related to the field of ice adhesion, specifically, to melting ice between freezer packages.
Ice adhesion to freezer packages causes various types of problems. Food, medical and biological materials, and other materials often are stored below the freezing temperature of water. The material is typically stored in freezer bags and various other types of freezer packages. Water vapor that condenses in a freezer and water from other sources freezes between the packages. As a result, adjacent packages are stuck together by ice adhering to adjacent outside surfaces of packages. Individual packages frozen to one or more other packages cannot be moved individually unless the ice is melted. Melting the ice to separate the packages raises the temperature of the material contained in the packages. This often results in undesired thawing of food, or otherwise raising the temperature of a package""s contents above an undesired or a critical temperature. Therefore, the package""s contents may be destroyed or rendered useless. Melting all of the ice between a large number of packages in a freezer by raising the freezer temperature causes downtime and an accumulation of liquid water, which must be removed from the freezer separately.
The invention helps to solve some of the problems mentioned above by providing systems and methods for melting ice at an ice interface and for preventing the formation of ice.
In one aspect of the invention, a system for both preventing ice and for melting ice on a freezer package includes a first electrode and a second electrode, the first electrode and the second electrode defining an interelectrode space for accommodating a freezer package. In another aspect, a system in accordance with the invention includes an AC power source for providing an AC voltage across the first and second electrodes. Typically, the AC voltage is a high-frequency voltage, with a frequency not less than about 1000 Hz. Preferably, the AC voltage has a frequency in a range of about from 10 kHz to 30 kHz. In still another aspect of the invention, the AC voltage does not significantly heat the contents of the freezer package or melt bulk ice. Typically, the AC voltage has an amplitude in a range of about from 10 to 1000 volts, but the voltage is 10 kV or higher in certain conditions.
In one aspect, a system further includes a freezer package located in the interelectrode space. In another aspect, the freezer package has a freezer package wall with an outer dielectric film and a continuous inner conductive layer contiguous to the outer dielectric film. In still another aspect, a freezer package wall has a first portion proximate to the first electrode so that the AC voltage generates an alternating electric field between the first electrode and the first portion strong enough to melt ice.
In another aspect, heating of the contents of a freezer package is insignificant, amounting generally to less than 1 calorie per gram, and typically less than {fraction (1/10)} calorie per gram.
In another aspect of the invention, a system further includes a plurality of freezer packages arranged in a stack with a first freezer package proximate to the first electrode, and a last freezer package proximate to the second electrode, each of the plurality of freezer packages including an outer dielectric film and a continuous inner conductive layer contiguous to the outer dielectric film. A freezer package in accordance with the invention is useful for holding a variety of types of contents; for example, food and biological materials.
In another aspect, the invention further includes a freezer with a housing, and a first electrode and a second electrode that define an interelectrode space. Preferably, the first electrode is movable. In another aspect, a freezer system includes an AC power source for providing an AC voltage across the first and second electrodes with a frequency not less than about 1000 Hz, which AC voltage does not heat the contents of a freezer package. In one aspect, the second electrode is integral with the freezer housing. In another aspect, the second electrode is mounted in a freezer space of a conventional freezer or it is a movable electrode. In another aspect, a freezer system in accordance with the invention further includes a freezer package located in the interelectrode space. The freezer package has a freezer package wall with an outer dielectric film and a continuous inner conductive layer contiguous to the outer dielectric film. In another aspect, the freezer package wall has a first portion proximate to the first electrode so that the AC voltage generates an alternating electric field between the first electrode and the first portion strong enough to melt ice. In still another aspect, a freezer system further includes a plurality of freezer packages arranged in a stack with a first freezer package proximate to the first electrode, and a last freezer package proximate to the second electrode, each of the plurality of freezer packages including an outer dielectric film and a continuous inner conductive layer contiguous to the outer dielectric film.
In one aspect of the invention, a system for melting ice includes a first electrode and a second electrode, the first electrode and the second electrode defining an interelectrode space between the first electrode and the second electrode. The system may include a conductive layer located in the interelectrode space and electrically insulated from the first and second electrodes. In another aspect, a conductive layer is located proximate to the first or second electrode. In another aspect, a system includes an outer dielectric film that electrically insulates the conductive layer from the first and second electrodes and from ice and liquid water.
The invention also provides a method for preventing ice and for melting ice. A method in accordance with the invention includes a step of generating a high-frequency alternating electric field that prevents the formation of ice or melts interfacial ice without significantly heating bulk ice, bulk dielectric material, or contents of a freezer package. The step of generating a high-frequency alternating electric field may include applying an AC voltage with a frequency not less than about 1000 Hz across a first electrode and a second electrode. Typically, the AC voltage has an amplitude in a range of about from 10 to 1000 volts, but the voltage is 10 kV or higher in certain conditions. Typically, a method in accordance with the invention is used to prevent ice or melt ice on and between one or more freezer packages or other objects, the bulk of which is dielectric. Preferably, the objects, such as freezer packages, are located in an interelectrode space between the first electrode and the second electrode. In another aspect, the step of generating a high-frequency alternating electric field in the ice includes generating conductivity AC in an inner conductive layer, the inner conductive layer electrically insulated from the ice and the first and second electrodes. In other aspects, the inner conductive layer is contiguous to an outer dielectric film, and the outer dielectric film is located proximate to the first electrode and between the first electrode and the inner conductive layer.